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United States Patent |
5,791,348
|
Aung
,   et al.
|
August 11, 1998
|
Automatic blood pressure measuring system
Abstract
An automatic blood pressure measuring system employs an oscillometric
method, a cuff applying pressure to an arterial vessel and then gradually
reducing the pressure. On a distal side of the cuff, as seen from the
heart of the subject, a pulse wave sensor presses against a distal section
of the vessel. If the pulse wave sensor detects a pulse wave from the
distal section of the vessel after the force applied by the cuff reaches a
first target value, indicating that the initial pressure was
insufficiently low, the force is increased to a second target value. After
determining a relationship between the blood pressure and the magnitude of
the pulse wave detected by the pulse wave sensor, blood pressure can be
monitored by the pulse wave sensor.
Inventors:
|
Aung; Ye (Komaki, JP);
Nishibayashi; Hideo (Inuyama, JP)
|
Assignee:
|
Colin Electronics Co., Ltd. (Aichi-ken, JP)
|
Appl. No.:
|
592611 |
Filed:
|
January 26, 1996 |
Foreign Application Priority Data
Current U.S. Class: |
600/493; 600/494; 600/495 |
Intern'l Class: |
A61B 005/00 |
Field of Search: |
128/668,677,680-3,687,672
|
References Cited
U.S. Patent Documents
4696151 | Sep., 1987 | Utsunomiya et al. | 128/682.
|
4870973 | Oct., 1989 | Ueno.
| |
4872461 | Oct., 1989 | Miyawaki | 128/682.
|
4905704 | Mar., 1990 | Walloch | 128/681.
|
4924874 | May., 1990 | Murase.
| |
4928701 | May., 1990 | Harada et al. | 128/681.
|
5099853 | Mar., 1992 | Uemura et al. | 128/681.
|
Foreign Patent Documents |
0 298 620 | Jan., 1989 | EP.
| |
0 333 332 | Sep., 1989 | EP.
| |
0 401 382 | Dec., 1990 | EP.
| |
Primary Examiner: Nasser; Robert L.
Attorney, Agent or Firm: Oliff & Berridge
Parent Case Text
This is a Continuation of application Ser. No. 07/829,325 filed Feb. 3,
1992, now abandoned.
Claims
What is claimed is:
1. An automatic blood pressure measuring system for measuring a blood
pressure of a living subject by an oscillometric method in which a blood
pressure is determined by utilizing a pulse wave comprising pulses
produced from an arterial vessel of the subject in synchronism with a
heartbeat of the subject, the apparatus comprising:
an inflatable cuff adapted to be wound around an upper arm of a subject,
for pressing said upper arm and thereby pressing a brachial artery
extending in said upper arm of said subject;
regulating means for regulating a pressing force of said cuff;
oscillometric blood-pressure measuring means comprising control means for
controlling said regulating means to increase said pressing force of said
cuff to a first target force, a first pulse wave sensor associated with
said cuff, for collecting pulses of a first pressure pulse wave which are
produced from said brachial artery and transmitted to said cuff when said
pressing force is decreased from said first target force, and means for
determining a blood pressure of said subject by an oscillometric method
using the collected pulses;
a second pulse wave sensor for detecting a second pressure pulse wave from
a radial artery which is continuous with said brachial artery of said
subject and is located on a distal side of said brachial artery as seen
from the heart of said subject, said second pulse wave sensor being
adapted to be pressed against said radial artery via skin tissue of said
subject for detecting the second pressure pulse wave therefrom, said
second pulse wave sensor being apart from said cuff;
first determining means for determining a magnitude of the second pressure
pulse wave which is detected from said radial artery by said second pulse
wave sensor when said brachial artery is not pressed by said cuff;
second determining means for determining a relationship between blood
pressure and pulse magnitude by using the blood pressure measured by said
measuring means and the determined magnitude of said second pressure pulse
wave;
third determining means for determining a magnitude of each of pulses of
said second pressure pulse wave which are detected from said radial artery
by said second pulse wave sensor after the determination of said
relationship and when said brachial artery is not pressed by said cuff;
fourth determining means for determining a blood pressure of said subject
by using the determined relationship and the determined magnitude of said
each pulse; and
increasing means for increasing said pressing force to a second target
force greater by a predetermined amount than said first target force, in
response to detection of presence of the second pressure pulse wave by
said second pulse wave sensor from said radial artery after said
regulating means has increased said pressing force of said cuff to said
first target force for pressing said brachial artery and before said
measuring means determines said blood pressure of said subject, wherein
said first pulse wave sensor of said measuring means starts collecting the
pulses transmitted to said cuff, if said second pulse wave sensor does not
detect the second pressure pulse wave from said radial artery before a
predetermined time has passed after said pressing force of said cuff
begins to decrease from said first target force.
2. The system as set forth in claim 1, wherein said increasing means
continues to increase said pressing force by increments of said
predetermined amount until said second pulse wave sensor does not detect
the second pressure pulse wave from said radial artery.
3. The system as set forth in claim 1, further comprising means for
supplying said cuff with pressurized fluid for inflating the cuff and
thereby pressing said upper arm and said brachial artery.
4. The system as set forth in claim 1, wherein said measuring means
determines a systolic and a diastolic blood pressure of said subject, said
first determining means determines a maximum and a minimum magnitude of a
pulse of said second pressure pulse wave detected by said pulse wave
sensor, said second determining means determines the blood pressure-pulse
magnitude relationship by using the systolic and diastolic blood pressures
determined by said measuring means and the determined maximum and minimum
pulse magnitudes, said third determining means determines a maximum and a
minimum magnitude of said each second pulse of said second pressure pulse
wave detected by said pulse wave sensor after the determination of said
blood pressure-pulse magnitude relationship, and said fourth determining
means determines a systolic and a diastolic blood pressure of said subject
by using said blood pressure-pulse magnitude relationship and said maximum
and minimum magnitude of said each pulse of said second pressure pulse
wave.
5. The system as set forth in claim 1, wherein said measuring means
determines said blood pressure of said subject at predetermined regular
intervals of time, said second determining means updates said blood
pressure-pulse magnitude relationship by using each of the blood pressures
determined at said regular intervals and a determined magnitude of said
second pressure pulse wave, said third determining means determines a
magnitude of each of pulses of said second pressure pulse wave detected
after each updating of said relationship, and said fourth determining
means determines a blood pressure of said subject by using said each
updated relationship and the determined magnitude of said each pulse.
6. The system as set forth in claim 1, wherein said second determining
means determines said blood pressure-pulse magnitude relationship such
that blood pressure is a linear function of pulse magnitude.
7. The system as set forth in claim 1, further comprising display means for
displaying said blood pressure determined by said measuring means and said
blood pressure determined by said fourth determining means.
8. An automatic blood pressure measuring system for measuring a blood
pressure of a living subject by an oscillometric method in which a blood
pressure is determined by utilizing a pulse wave comprising pulses
produced from an arterial vessel of the subject in synchronism with a
heartbeat of the subject, the apparatus comprising:
an inflatable cuff adapted to be wound around an upper arm of a subject,
for pressing said upper arm and thereby pressing a brachial artery
extending in said upper arm of said subject;
regulating means for regulating a pressing force of said cuff;
oscillometric blood-pressure measuring means comprising control means for
controlling said regulating means to increase said pressing force of said
cuff to a first target force, a first pulse wave sensor associated with
said cuff, for collecting pulses of a first pressure pulse wave which are
produced from said brachial artery and transmitted to said cuff when said
pressing force is decreased from said first target force, and means for
determining a blood pressure of said subject by an oscillometric method
using the collected pulses;
a second pulse wave sensor for detecting a second pressure pulse wave from
a radial artery which is continuous with said brachial artery of said
subject and is located on a distal side of said brachial artery as seen
from the heart of said subject, said second pulse wave sensor being
adapted to be pressed against said radial artery via skin tissue of said
subject for detecting the second pressure pulse wave therefrom, said
second pulse wave sensor being apart from said cuff;
first determining means for determining a magnitude of the second pressure
pulse wave which is detected from said radial artery by said second pulse
wave sensor when said brachial artery is not pressed by said cuff;
second determining means for determining a relationship between blood
pressure and pulse magnitude by using the blood pressure measured by said
measuring means and the determined magnitude of said second pressure pulse
wave;
third determining means for determining a magnitude of each of pulses of
said second pressure pulse wave which are detected from said radial artery
by said second pulse wave sensor after the determination of said
relationship and when said brachial artery is not pressed by said cuff;
fourth determining means for determining a blood pressure of said subject
by using the determined relationship and the determined magnitude of said
each pulse; and
increasing means for increasing said pressing force to a second target
force greater by a predetermined amount than said first target force, in
response to detection of presence of the second pulse wave by said second
pulse wave sensor from said radial artery after said regulating means has
increased said pressing force of said cuff to said first target force for
pressing said brachial artery and before said measuring means determines
said blood pressure of said subject, wherein any second pulse wave
detected by the second pulse wave sensor before passing of a predetermined
time is excluded from the blood pressure determination.
9. The system as set forth in claim 8, wherein said increasing means
continues to increase said pressing force by increments of said
predetermined amount until said second pulse wave sensor does not detect
the second pressure pulse wave from said radial artery.
10. The system as set forth in claim 8, further comprising means for
supplying said cuff with pressurized fluid for inflating the cuff and
thereby pressing said upper arm and said brachial artery.
11. The system as set forth in claim 8, wherein said measuring means
determines a systolic and a diastolic blood pressure of said subject, said
first determining means determines a maximum and a minimum magnitude of a
pulse of said second pressure pulse wave detected by said second pulse
wave sensor, said second determining means determines the blood
pressure-pulse magnitude relationship by using the systolic and diastolic
blood pressures determined by said measuring means and the determined
maximum and minimum pulse magnitudes, said third determining means
determines a maximum and a minimum magnitude of said each pulse of said
second pressure pulse wave detected by said second pulse wave sensor after
the determination of said blood pressure-pulse magnitude relationship, and
said fourth determining means determines a systolic and a diastolic blood
pressure of said subject by using said blood pressure-pulse magnitude
relationship and said maximum and minimum magnitudes of said each pulse of
said second pressure pulse wave.
12. The system as set forth in claim 8, wherein said measuring means
determines said blood pressure of said subject at predetermined regular
intervals of time, said second determining means updates said blood
pressure-pulse magnitude relationship by using each of the blood pressures
determined at said regular intervals and a determined magnitude of said
second pressure pulse wave, said third determining means determines a
magnitude of each of pulses of said second pressure pulse wave detected
after each updating of said relationship, and said fourth determining
means determines a blood pressure of said subject by using said each
updated relationship and the determined magnitude of said each pulse.
13. The system as set forth in claim 8, wherein said second determining
means determines said blood pressure-pulse magnitude relationship such
that blood pressure is a linear function of pulse magnitude.
14. The system as set forth in claim 8, further comprising display means
for displaying said blood pressure determined by said measuring means and
said blood pressure determined by said fourth determining means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an automatic blood pressure measuring
system of the oscillometric type and more particularly to such an
apparatus which is adapted to measure a blood pressure of a living subject
when the pressing force applied to an artery of the subject is decreased.
2. Related Art Statement
There is known an automatic blood pressure measuring system for measuring a
blood pressure of a living subject by the oscillometric method in which a
blood pressure of the subject is determined by utilizing a pulse wave
consisting of pulses produced from an artery of the subject in synchronism
with heartbeat of the subject. The known apparatus includes (a) a pressing
device pressing a body portion of a subject and thereby pressing an artery
extending in the body portion of the subject, (b) pressure regulating
means regulating the pressing force or pressure produced by the pressing
device, and (c) determining means controlling the regulating means to
increase the pressure of the pressing device to a target pressure (for
example, 180 mmHg, or a pressure higher by a suitable amount than a
systolic blood pressure of the subject measured in a preceding cycle),
collecting pulses of a pulse wave which are produced from the artery and
transmitted to the pressing device when the pressure applied to the artery
is decreased from the target pressure, and determining a blood pressure of
the subject by using the collected pulses. This apparatus is adapted to
determine, as a mean blood pressure of the subject, a pressure applied to
the artery at the time of detection of a pulse having the greatest
amplitude of the amplitudes of the pulses collected during the pressure
decreasing operation. In addition, the apparatus determines, as a systolic
blood pressure of the subject, a pressure applied to the artery at the
time of an inflection point of a curve representing variation of the pulse
amplitudes with respect to the pressure applied to the artery which point
is located on a higher-pressure side of the mean blood pressure, and as a
diastolic blood pressure a pressure at the time of an inflection point of
the curve which point is located on a lower-pressure side of the mean
blood pressure.
However, the known oscillometric blood pressure measuring apparatus suffers
from the problem that, if an actual systolic blood pressure of the subject
is higher than the target pressure, or if the actual systolic blood
pressure is lower than the target pressure but higher than a pressure at
the time when the determining means starts collecting the pulses of the
pulse wave transmitted to the pressing device during the pressure
decreasing operation, the apparatus cannot measure the systolic blood
pressure of the subject because the target pressure is insufficiently low.
In the case where the apparatus is of a type which determines a systolic
blood pressure immediately after determining a mean blood pressure during
the pressure decreasing operation, the apparatus cannot identify that the
target pressure is insufficiently low until the pressure applied to the
artery is decreased to a level equal to the mean blood pressure.
Meanwhile, in the case where the apparatus is of a type which determines a
blood pressure by using the pulse wave data obtained during the pressure
decreasing operation after the pressure decreasing operation has been
completed, the apparatus cannot identify that the target pressure is
insufficient until the pressure decreasing operation is completed.
Therefore, if the target pressure is insufficient, both of these apparatus
are required to effect the blood pressure measuring operation again. This
leads to increasing the time necessary for completing the blood pressure
measuring operation.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an automatic
blood pressure measuring system for, by using the oscillometric method,
measuring a blood pressure of a subject when the pressing force applied to
an artery of the subject is decreased from a target force, which system
finds insufficiency of the target force and eliminates the insufficiency
before the blood pressure measurement and thereby effects the blood
pressure measurement in a reduced time.
The above object has been achieved by the present invention, which provides
an automatic blood pressure measuring system for measuring a blood
pressure of a living subject by the oscillometric method in which a blood
pressure is determined by utilizing a pulse wave consisting of pulses
produced from an arterial vessel of the subject in synchronism with
heartbeat of the subject, the apparatus comprising (1) pressing means for
pressing a body portion of a subject and thereby pressing an arterial
vessel extending in the body portion of the subject, (2) regulating means
for regulating the pressing force of the pressing means, (3) determining
means for controlling the regulating means to increase the pressing force
of the pressing means to a first target force, collecting pulses of a
pulse wave which are produced from the arterial vessel and transmitted to
the pressing means when the pressing force is decreased from the first
target force, and determining a blood pressure of the subject by using the
collected pulses, (4) detecting means for detecting a pulse wave from a
section of the arterial vessel located on a distal side of the pressing
means as seen from the heart of the subject, and (5) increasing means for,
if the detecting means detects the pulse wave from the distal arterial
vessel after the regulating means has increased the pressing force of the
pressing means to the first target force and before the determining means
determines the blood pressure of the subject, increasing the pressing
force to a second target force greater by a predetermined amount than the
first target force.
In the automatic blood pressure measuring system of the oscillometric type
constructed as described above, the detecting means detects a pulse wave
from a section of the arterial vessel pressed by the pressing means which
section is located on a distal side of the pressing means as seen from the
heart of the subject, and the increasing means increases, if the detecting
means detects the pulse wave from the distal arterial vessel after the
regulating means has increased the pressing force of the pressing means to
the first target force and before the determining means determines the
blood pressure of the subject, the pressing force to a second target force
greater by a predetermined amount than the first target force. That the
detecting means has detected the pulse wave from the distal arterial
vessel after the pressing force has been increased to the first target
force and before the blood pressure is determined, means that the first
target force is insufficiently low. Thus, the present system identifies
whether or not the first target force is insufficiently low, before the
blood pressure of the subject is determined. If the first target force is
found to be insufficient, the system or increasing means thereof increases
the pressing force of the pressing means to the second target force
greater by a predetermined additional pressing force than the first target
force, thereby eliminating the insufficiency of the pressing force (i.e.,
first target force) applied to the artery before the blood pressure
determination. Thus, the present system completes the blood pressure
measuring operation in a reduced time even as compared with a conventional
apparatus of the type which identifies whether or not a target pressing
force is insufficient after the pressing force applied to an artery of a
subject is decreased from the target force to a pressing force
corresponding to a mean blood pressure of the subject and, if the target
force is found to be insufficient, effects the blood pressure measuring
operation all over again.
According to a preferred feature of the present invention, the increasing
means continues to increase the pressing force by increments of the
predetermined amount until the detecting means does not detect a pulse
wave from the distal arterial vessel.
According to another feature of the present invention, the determining
means starts collecting the pulses transmitted to the pressing means, at a
time when a predetermined time has passed after the decreasing of the
pressing force from the first target force is started.
According to yet another feature of the present invention, the pressing
means comprises an inflatable cuff which is adapted to be wound around the
body portion of the subject, and means for supplying the cuff with
pressurized fluid for inflating the cuff an thereby pressing the body
portion and the arterial vessel.
In a preferred embodiment of the present invention, the detecting means
comprises a pulse wave sensor which is adapted to be pressed against the
distal arterial for detecting a pressure pulse wave therefrom.
According to a feature of the above embodiment of the invention, the system
further comprising first means for determining a magnitude of the pressure
pulse wave which is detected by the pulse wave sensor when the arterial
vessel is not pressed by the pressing means, second means for determining
a relationship between blood pressure and pulse magnitude by using the
blood pressure determined by the determining means and the determined
magnitude of the pressure pulse wave, third means for determining a
magnitude of each of pulses of the pressure pulse wave which are detected
by the pulse wave sensor after the determination of the relationship, and
fourth means for determining a blood pressure of the subject by using the
determined relationship and the determined magnitude of the each pulse.
According to another feature of the above embodiment of the invention, the
determining means determines a systolic and a diastolic blood pressure of
the subject, the first means determines a maximum and a minimum magnitude
of a pulse of the pressure pulse wave detected by the pulse wave sensor,
the second means determines the blood pressure-pulse magnitude
relationship by using the systolic and diastolic blood pressures
determined by the determining means and the determined maximum and minimum
pulse magnitudes, the third means determines a maximum and a minimum
magnitude of the each pulse of the pressure pulse wave detected by the
pulse wave sensor after the determination of the blood pressure-pulse
magnitude relationship, and the fourth means determines a systolic and a
diastolic blood pressure of the subject by using the blood pressure-pulse
magnitude relationship and the maximum and minimum magnitude of the each
pulse of the pressure pulse wave.
According to yet another feature of the above embodiment of the invention,
the determining means determines the blood pressure of the subject at
predetermined regular intervals of time, the second means updates the
blood pressure-pulse magnitude relationship by using each of the blood
pressures determined at the regular intervals and a determined magnitude
of the pressure pulse wave, the third means determines a magnitude of each
of pulses of the pressure pulse wave detected after each updating of the
relationship, and the fourth means determines a blood pressure of the
subject by using the each updated relationship and the determined
magnitude of the each pulse.
According to a further feature of the above embodiment of the invention,
the second means determines the blood pressure-pulse magnitude
relationship such that blood pressure is a linear function of pulse
magnitude.
According to a preferred feature of the above embodiment of the invention,
the system further comprises display means for displaying the blood
pressure determined by the determining means and the blood pressure
determined by the fourth means.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and optional objects, features and advantages of the present
invention will be better understood by reading the following detailed
description of the presently preferred embodiment of the invention when
considered in conjunction with the accompanying drawings, in which:
FIG. 1 a diagrammatic view of an automatic blood pressure measuring system
of the oscillometric type to which the present invention is applied;
FIG. 2 is a flow chart representing a part of the control programs
according to which the system of FIG. 1 is operated; and
FIG. 3 is a flow chart representing another part of the control programs
according to which the system of FIG. 1 is operated.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1, there is shown an automatic blood pressure
monitor system of the oscillometric type embodying the present invention.
In the figure, reference numeral 10 designates an inflatable cuff formed
of rubber. The cuff 10 has a tube-like configuration. The cuff 10 is wound
around, for example, an upper portion 13 of an arm 12 of a living subject.
The cuff 10 serves as pressing means for pressing the upper arm 13. A
pressure sensor 14, a selector valve 16, and an air pump 18 are connected
via piping 20 to the cuff 10. The air pump 18 supplies the cuff 10 with
pressurized air, thereby increasing an air pressure in the cuff 10. The
pressure sensor 14 detects the air pressure in the cuff 10 (hereinafter,
referred to as the "cuff pressure P"), and generates a pressure signal SP
representing the detected cuff pressure P, to a first and a second filter
circuit 22, 24. The first filter circuit 22 includes a low-pass filter
which, upon reception of the pressure signal SP, transmits only a cuff
pressure signal SK representing a static pressure in the cuff 10. The cuff
pressure signal SK is supplied to a control device 28 via a first analog
to digital (A/D) converter 26. The second filter circuit 24 includes a
band-pass filter which, upon supply of the pressure signal SP, transmits
only a pulse wave signal SM.sub.1 representing a pressure pulse wave
consisting of pulses produced from a brachial artery in synchronism with
heartbeat of the subject and transmitted to the cuff 10. The pulse wave
signal SM.sub.1 is supplied to the control device 28 via a second A/D
converter 30. The selector valve 16 is adapted to selectively be placed in
a first position thereof (the INFLATION position) in which the valve 16
allows the cuff pressure P to be increased, in a second position thereof
(the SLOW-DEFLATION position) in which the valve 16 allows the pressure P
to be decreased at a low rate, or a third position thereof (the
RAPID-DEFLATION position) in which the valve 16 allows the pressure P to
be decreased at a high rate. In the present embodiment, the selector valve
16, air pump 18, and other elements cooperate with each other to serve as
regulating means for regulating the pressing force (cuff pressure P) of
the pressing means (cuff 10).
The control device 28 includes a so-called microcomputer consisting
essentially of a central processing unit (CPU), a read only memory (ROM),
a random access memory (RAM), and an input and output port (I/O port). The
CPU processes input signals according to control programs pre-stored in
the ROM by utilizing the temporary-storage function of the RAM and
produces, via the I/O port, drive signals to respective drive circuits
(not shown) provided for the selector valve 16 and the air pump 18. In
this way, the control device 28 controls the selector valve 16 and air
pump 18 for regulating the cuff pressure P. The control device 28 controls
the regulating means 16 and 18 for increasing the cuff pressure P to a
target pressure, Pm.sub.a, and, if a pulse wave sensor 34 (described
later) detects a pulse wave after the cuff pressure P has been increased
to the target pressure Pm.sub.a and before blood pressure determination is
effected, the control device 28 controls the regulating means to increase
the cuff pressure P to a second target pressure, Pm.sub.b, higher by a
predetermined amount than the first target pressure Pm.sub.a. In addition,
the control device 28 collects pulse wave, or pulses thereof, produced
from the brachial artery and transmitted to the cuff 10 when the cuff
pressure P is decreased from the first or second target pressure Pm.sub.a
or Pm.sub.b, and determines a mean, a systolic and a diastolic blood
pressure of the subject by using the collected pulses. The control device
28 commands a display 32 such as a cathode ray tube (CRT) to indicate the
determined pressure values. The control device 28 iteratively effects this
blood pressure determination at predetermined regular intervals of time.
In the present embodiment, the control device 28 serves as increasing
means for increasing the cuff pressure P to the second target pressure
Pm.sub.b higher by the predetermined amount than the first target pressure
Pm.sub.a.
The pulse wave sensor 34 is connected to the control device 28 via a third
A/D converter 36. The pulse wave sensor 34 is secured to the inside
surface of an elongate wrist band 38 having a pair of fasteners (not
shown) at opposite ends thereof. The wrist band 38 is wound around a wrist
40 of the same arm 12 as the arm pressed by the cuff 10, such that the
pulse wave sensor 34 is positioned over the radial artery that is
continuous with the brachial artery pressed by the cuff 10 and is located
on the distal side of the cuff 10 as seen from the heart of the subject.
With the fasteners of the wrist band 38 being fastened with each other
around the wrist 40, the pulse wave sensor 34 is pressed with a suitable
pressure against the radial artery via skin tissue. The pulse wave sensor
34 is constituted by, for example, a semiconductor strain gauge or a
piezoelectric element. The pulse wave sensor 34 detects a pressure pulse
wave (hereinafter, referred to as the "distal pulse wave") produced from
the radial artery located on the distal side of the brachial artery
pressed by the cuff 10. Like the pulse wave transmitted to the cuff 10,
the distal pulse wave consists of pulses produced in synchronism with
heartbeat of the subject. The pulse wave sensor 34 generates a pulse wave
signal SM.sub.2 representing the detected distal pulse wave, to the
control device 28 via the third A/D converter 36. In the present
embodiment, the pulse wave sensor 34 and the wrist band 38 cooperate with
each other to serve as detecting means for detecting the distal pulse
wave.
The control device 28 determines a maximum and a minimum magnitude of a
pulse of the distal pulse wave detected by the pulse wave sensor 34,
according to control programs pre-stored in the ROM, and determines a
relationship (e.g., a linear function) between blood pressure and pulse
magnitude by using the determined maximum and minimum pulse magnitudes and
the systolic and diastolic blood pressures actually measured using the
cuff 10. According to the blood pressure-pulse magnitude relationship, the
control device 28 continuously determines a systolic and a diastolic blood
pressure of the subject by using a maximum and a minimum magnitude of each
of pulses of the distal pulse wave detected by the pulse wave sensor 34
after determination of the relationship, and commands the display 32 to
indicate the blood pressure values determined with respect to the each
pulse.
Next, there will be described the operation of the present monitor system
by reference to the flow charts of FIGS. 2 and 3.
Upon application of electric power to the monitor system, the system is
initialized, and the control of the CPU of the control device 28 starts
with Step S1 to identify whether or not an ON/OFF switch (not shown) has
been operated to its ON position. If an negative judgement (NO) is made in
Step S1, Step S1 is repeated. On the other hand, if an affirmative
judgement (YES) is made in Step S1, the control of the CPU proceeds with
Step S2 to place the selector valve 16 in its INFLATION position and
activate the air pump 18 so as to increase the cuff pressure P to a
predetermined, initial target pressure, Pm, (e.g., 180 mmHg) and
subsequently to deactivate the air pump 18. Step S2 is followed by Step S3
to place the selector valve 16 from the INFLATION position to the
SLOW-DEFLATION position so as to start decreasing the cuff pressure P at a
predetermined, low rate.
Step S3 is followed by Step S4 to identify whether or not the pulse wave
sensor 34 has detected the distal pulse wave. If the initial target
pressure Pm is higher than a systolic blood pressure of the subject and
therefore the blood flow through the brachial artery is completely stopped
under the pressure produced by the cuff 10, a negative judgement is made
in Step S4. In this case, the control goes to Step S5 to identify whether
or not an appropriate time has passed from the starting of the cuff
pressure decreasing operation. This appropriate time may be a
predetermined time duration measured from the starting of the cuff
pressure decreasing operation, a time duration necessary for a
predetermined number of pulses to occur, or a time duration necessary for
the cuff pressure P to be decreased by a predetermined amount. If the
appropriate time has not passed and therefore a negative judgement is made
in Step S5, Steps S4 and S5 are repeated. On the other hand, if the time
has passed and an affirmative judgement is produced in Step S5, the
control goes to Step S8 to start reading in pulses of the pulse wave
produced from the brachial artery and transmitted to the cuff 10. That is,
the control device 28 does not read in pulses of the pulse wave during the
above-indicated appropriate time after the starting of the cuff pressure
decreasing operation. The pulses (that is, electric signal SM.sub.1) read
in in Step S8 are stored for being used for the blood pressure
determination in Step S10.
On the other hand, if the pulse wave sensor 34 has detected the distal
pulse wave during the above-indicated appropriate time and therefore an
affirmative judgement is made in Step S4, that means that a target
pressure, Pm.sub.a, (target pressure Pm for the initial control cycle)
from which the cuff pressure decreasing operation started, that is, a cuff
pressure from which the pulses collecting operation is started in Step S8,
is lower than a systolic blood pressure of the subject, that is,
insufficiently low. Consequently, the control goes to Steps S6 and S7. In
Step S6, a predetermined pressure amount, .DELTA.P, (e.g., 10 mmHg) is
added to the first target pressure Pm.sub.a for the present control loop
so as to provide a second target pressure Pm.sub.b, which is to be used as
the first target pressure Pm.sub.a if another affirmative judgement is
made with respect thereto in Step S4 in the following control loop. Step
S6 is followed by Step S7 to place the selector valve 16 from the
SLOW-DEFLATION position to the INFLATION position and activate the air
pump 18. Subsequently, the control goes back to Step S3 and the following
steps. In this control loop, if another affirmative judgement is made in
Step S4, the control goes to Steps S6 and S7 to increase the cuff pressure
P to a new second target pressure Pm.sub.b higher by the predetermined
amount .DELTA.P than the first target pressure Pm.sub.a, that is, the cuff
pressure at the time of starting of the cuff pressure decreasing operation
in Step S3 at the present control loop, that is, the second target
pressure Pm.sub.b determined in Step S7 at the preceding control loop.
Subsequently, in Step S3 at the following control loop, the cuff pressure
P is decreased from a new first target pressure Pm.sub.a, that is, the
above-indicated new second target pressure Pm.sub.b. Thus, the present
monitor system identifies whether or not the first target pressure
Pm.sub.a where the cuff pressure decreasing operation is started is
insufficiently low, after the cuff pressure decreasing operation has been
started and before the blood pressure determination or, more specifically,
the pulses collecting operation is started. If the first target pressure
Pm.sub.a is found to be insufficiently low, the monitor system continues
to increase the cuff pressure P up to a pressure level sufficiently higher
than the systolic blood pressure.
After in Step S8 the control device 28 starts reading in pulses of the
pulse wave transmitted to the cuff 10, the control goes to Step S9 to
identify whether or not the control device 28 has read in one pulse (that
is, signal SM.sub.1 representing one pulse) of the pulse wave transmitted
to the cuff 10. If a negative judgement is made in Step S9, Steps S8 and
S9 are repeated. On the other hand, if the control device 28 has read in
one pulse of the pulse wave and therefore an affirmative judgement is made
in Step S9, the control goes to Step S10 to effect the blood pressure
determine routine. This routine is a well-known oscillometric blood
pressure measure algorithm in which mean, systolic and diastolic blood
pressures are determined by utilizing variation of respective amplitudes
of the detected pulses with respect to variation in the cuff pressure P.
More specifically described, the control device 28 finds a pulse having
the greatest amplitude of the amplitudes of the pulses detected during the
cuff pressure decreasing operation (hereinafter, abbreviated to the
"maximum pulse"), and determines as a mean blood pressure of the subject a
cuff pressure at the time of detection of the maximum pulse. In addition,
the control device 28 determines as a systolic blood pressure of the
subject a cuff pressure at the time of an inflection point of a curve
representing the variation of the pulse amplitudes which point is
positioned on a higher-pressure side of the mean blood pressure, and as a
diastolic blood pressure of the subject a cuff pressure at the time of an
inflection point of the curve positioned on a lower-pressure side of the
mean blood pressure. Subsequently, the control goes to Step S11 to
identify whether or not the blood pressure determination has been
completed. If a negative judgement is made in Step S11, Steps S8 through
S11 are repeated. On the other hand, if the blood pressure determination
has been completed and therefore an affirmative judgement is made in Step
S11, the control of the CPU goes to Step S12 to switch the selector valve
16 from the SLOW-DEFLATION position to the RAPID-DEFLATION position so as
to decrease the cuff pressure P at a high rate. Subsequently, the control
proceeds to Step S13 to indicate the determined blood pressure values on
the display 32.
Next, the control of the CPU goes to Step S14 to read in one pulse of the
distal pulse wave detected by the pulse wave sensor 34, that is, electric
signal SM.sub.2 representing the pulse. Subsequently, the control goes to
Step S15 to determine a relationship between blood pressure and magnitude
of pulse (that is, magnitude of signal SM.sub.2). More specifically
described, the control device 28 determines a maximum and a minimum
magnitude (that is, upper and lower peak magnitudes) of the pulse detected
in Step S14, and determines a linear function by using the determined
maximum and minimum pulse magnitudes and the systolic and diastolic blood
pressures determined in Step S10. This method is described in detail in
U.S. Pat. No. 5,139,026, the assignee of which is the assignee of the
present application.
Step S15 is followed by Step S16 to identify whether or not the pulse wave
sensor 34 has detected one pulse of the distal pulse wave. If a negative
judgement is made in Step S16, Step 16 is repeated. Meanwhile, if the
pulse wave sensor 34 has detected a pulse and accordingly an affirmative
judgement is made in Step S16, the control goes to Step S17 to determine a
maximum and a minimum magnitude of the detected pulse and subsequently to
Step S18 to determine a systolic and a diastolic blood pressure of the
subject by using the blood pressure-pulse magnitude relationship
determined in Step S15 and the maximum and minimum pulse magnitudes
determined in Step S17. Further, in Step S19, the control device 28
commands the display 32 to indicate the determined blood pressure values.
Subsequently, the control goes to Step S20 to identify whether or not the
ON/OFF switch has been operated to its OFF position. If a negative
judgement is made in Step S20, the control goes to Step S21 to identify
whether or not a predetermined regular interval (e.g., 5 to 10 minutes)
has passed. If a negative judgement is made in Step S21, the control goes
back to Step S16 and the following steps to determine a systolic and a
diastolic blood pressure of the subject by using the relationship
determined in Step S15 and a maximum and a minimum magnitude of each of
pulses detected by the pulse wave sensor 34 after determination of the
relationship, and continuously indicate on the display 32 the blood
pressure values determined with respect to the each pulse. On the other
hand, if an affirmative judgement is made in Step S21, the control goes
back to Step S2 and the following steps to measure a systolic and a
diastolic blood pressure of the subject using the cuff 10 in Step 10,
update the blood pressure-pulse magnitude relationship in Step S15, and
monitor the blood pressure of the subject using the pulse wave sensor 34
in Step S18. Meanwhile, if the ON/OFF switch is operated to the OFF
position and an affirmative judgement is made in Step S20, the control
goes to Step S1 to wait for operation of the ON/OFF switch to the ON
position.
As is apparent from the foregoing description, in the present blood
pressure monitor system, the pulse wave sensor 34 is set over the radial
artery which is continuous with the brachial artery pressed by the cuff 10
and is located on the distal side of the cuff 10 as seen from the heart of
the subject, so that the sensor 34 detects the distal pulse wave from the
radial artery. If the pulse wave sensor 34 detects the distal pulse wave
after the cuff pressure P has been increased to the first target pressure
Pm.sub.a and before the control device 28 starts collecting pulses of the
pulse wave transmitted to the cuff 10, the monitor system identifies that
the first target pressure Pm.sub.a is insufficiently low. In this case,
the monitor system increases the cuff pressure P to the second target
pressure Pm.sub.b higher by the predetermined pressure amount than the
first target pressure Pm.sub.a and, by repeating this operation as needed,
the monitor system increases the cuff pressure P up to a pressure level
sufficiently higher than the systolic pressure of the subject. Thus, the
present system completes the blood pressure determination in a reduced
time as compared with a conventional apparatus of the type which does not
identify whether or not a target pressure is insufficiently low until cuff
pressure is decreased to a pressure level equal to a mean blood pressure
of the subject.
Since, in the present embodiment, whether the first target pressure
Pm.sub.a is insufficient or not is identified after the starting of the
cuff pressure decreasing operation and before the starting of the pulses
collecting operation, the blood pressure determination is completed in a
still shorter time than in a manner where the identification is made
before the starting of the cuff pressure decreasing operation. However, it
is possible to adapt the present embodiment to make this identification
before the starting of the cuff pressure decreasing operation.
In addition, in the present embodiment, the pulse wave sensor 34 provided
for monitoring the blood pressure of a subject serves also as the distal
pulse wave detecting means used for identifying whether the first target
pressure Pm.sub.a is insufficient or not. This arrangement contributes to
simplifying the construction of the monitor system.
While, in the illustrated embodiment, the pulse wave sensor 34 is pressed
on the wrist 40 with a pressing force produced by the band 38, it is
possible to use, in place of the band 40, an exclusive pressing device
disclosed in the above-indicated U.S. Pat. No. 5,139,026. This pressing
device includes a housing adapted to be set on, for example, a wrist with
the help of a band, and the pulse wave sensor is supported by the housing
so as to be advanceable from an open end of the housing. In this case, the
pressing force applied to the pulse wave sensor is adjusted by changing
air pressure in a chamber defined in the housing.
Although, in the illustrated embodiment, the pulse wave sensor 34 detects
the distal pulse wave from the radial artery, it is possible to use means
for detecting a pulse wave from a digital artery located at a more distal
position than the radial artery. Alternatively, it is possible to press
using a cuff a femoral artery and detect using a pulse wave sensor a pulse
wave from a dorsal artery of foot located on a distal side of the femoral
artery pressed by the cuff.
Furthermore, in place of the pulse wave sensor 34 detecting a pressure
pulse wave, it is possible to employ, as the distal pulse wave detecting
means, an oximeter which optically detects a blood oxygen saturation of
the subject. The blood oxygen saturation detected by the oximeter can be
used as distal pulse wave for identifying whether or not the first target
pressure Pm.sub.a is insufficiently low.
Although, in the illustrated embodiment, Steps S8 and S9 are effected after
Steps S3 through S7, it is possible to carry out Steps S8 and S9
concurrently with Steps S3 through S7.
The illustrated monitor system iteratively effects blood pressure
determinations at predetermined regular intervals of time by using the
cuff 10, and monitor the blood pressure of a subject by determining
systolic and diastolic blood pressures with respect to each of pulses of a
pulse wave detected by the pulse wave sensor 34. However, the principle of
the present invention is applicable to other types of blood pressure
measuring apparatus, for example, an apparatus of the type which uses a
pulse wave sensor exclusively for identifying whether or not the first
target pressure Pm.sub.a is insufficient or not. In this case, the
apparatus may be of the type which carries out the blood pressure
determination only one time in response to one-time operation of the
ON/OFF switch.
It is to be understood that the present invention may be embodied with
various changes, improvements and modifications that may occur to those
skilled in the art without departing from the scope and spirit of the
invention defined in the appended claims.
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